1. Field of the Invention
The present invention relates generally to protection devices, and particularly to protection devices having miswire protection.
2. Technical Background
Protective devices such as ground fault circuit interrupters (GFCIs) are well known in the art. Their intent is and always has been to protect the electrical power user from electrocution when hazardous ground fault currents are present.
Historical problems with these protective devices include the possibility of line/load miswiring in the field by an installer or the eventual failure of the solenoid driving device, typically a silicon controlled rectifier, which causes the interrupter device to become inoperable while electrical power is still present, even under hazardous ground fault conditions. A variety of methods are used to prevent or attempt to prevent miswiring with varying levels of success. Preventing the problems associated with a defective solenoid driving device is inherently more difficult. Labels and installation instruction sheets have been used to prevent miswiring, but can be ignored by the installer. Solenoid burn-out has been revealed by testing the protective device with a test button, but the result of the test can be ignored by the user.
Most GFCIs have test and reset buttons having associated instructions molded into the front cover of the device. The instructions typically require the user/homeowner to push the test button monthly. When depressed, the test button generates a current to simulate a fault condition. The device is not providing ground fault protection when the reset button fails to pop out. Accordingly, the user is instructed to replace the device. However, this approach has several drawbacks.
Of course, users routinely ignore the instructions printed on the cover of GFCI devices. If the device fails, the user is not aware that the device is not affording any protection. On the other hand, even if the user does press the button and discover that the device has failed, it may be some time before the user replaces the device.
Another drawback of the standard devices relates to the fact that a line-load miswire condition is often not tested by the test button. When a device is miswired, it may not protect the user from a fault condition even if it is functioning properly. The hazard will be present at the receptacle outlets even if the device is tripped. In other words, when a miswiring condition is present, the AC power is connected directly to the load terminals. The load terminals are typically connected to the user load terminals (i.e., the receptacles). When the device trips, the conductive path between the line terminals and load terminals is interrupted. However, since the load terminals and the user load terminals are still connected, the device fails to protect the user. In this case, the test and reset buttons may operate normally, giving the user a false sense of security.
In one approach that has been considered, a lock-out mechanism has been introduced such that the device will not reset if there is a line-load miswire condition. Power is denied to the load side circuit until the miswire condition is eliminated. Further, if the device is experiencing an internal fault such that the device is not operating properly, the device will likewise, not reset. One drawback to this condition is that it provides the user a disincentive to test. In other words, the user will feel inconvenienced if the device does not work after the test button is pushed. Further, this approach fails to address the scenario described above, when users fail to routinely use the test button.
In another approach that has been considered, a fused miswire circuit is disposed in the GFCI. If the device is miswired, the circuit induces a current simulating a fault condition, and the device trips. If the device is wired properly, the circuit again induces a current simulating a fault condition, and the device again trips. However, the current continues to flow until a fuse burns out. One drawback to this approach is that the miswire detection circuit may only be used once, and is forever disabled thereafter.
What is needed is a multi-shot method for testing mis-wiring. Further, a device is needed that eliminates any hazard at the receptacle outlets when the device is tripped.